Blind threaded fasteners are fasteners, either internally or externally threaded, that can be first installed into a hole in a panel with access to one side of the panel only, hence the term “blind”. Most of these fasteners contain three basic components: a head, an intermediate collapsible thin-walled shank, and an internally threaded region at the end. As depicted sequentially in FIGS. 1, 2, 3, and 4, the threaded area and a portion of the shank are first installed into the panel hole and then a compressive force is applied to the shank with a tool by pulling on the threaded region while supporting the head. This compression causes the shank to deform and buckle outwardly, creating what is known as a “bulb” on the side of the sheet opposite the head. The threaded tool member used to compress the shank is then removed, leaving the fastener permanently gripped to the panel being restrained by the head in one direction and the bulb in the other direction.
Presently available tools for applying the compressive load (upset force) to collapse the shank can be divided into two broad categories, spin-spin tools and spin-pull tools. Both types of tools utilize an anvil, also known as a nosepiece, from which a mandrel projects. Its function is to support the head of the fastener while the mandrel retracts or spins to force the insert toward the anvil. Spin-spin tools apply the compressive load to the shank by applying enough torque to a mandrel threaded into the fastener to produce the required load. Spin-spin tools are inexpensive, lightweight and simple to set up and use and are therefore generally preferred. However, because the upset force they can develop is limited, they generally cannot be used to install parts having thicker walls. Spin-pull tools spin the mating threaded member into position, then apply an axial pulling force by retracting the mandrel. The mandrel is then removed by spinning it in the opposite direction. Spin-pull tools are more complex and consequently more expensive and heavier than spin-spin tools. They are also more difficult to set up and require more maintenance. In spite of these disadvantages, spin-pull tools are the best available choice for thick-walled parts requiring higher compressive loads to form the bulb.
Both types of tools require time-consuming set-up steps with some degree of trial and error and a skilled operator. Spin-spin tools require mandrel length adjustment and adjustment to the stall torque. Spin-pull tools require an anvil adjustment relative to the fully-extended position of the mandrel and an adjustment to the stroke or pulling pressure. The set-up requirements of either type of tool represent lost time and require significant operator training. To enhance their operation, both types of tools often include control systems based on installing to a given torque or pulling to a given distance or a given force. In either case, these limits need to be determined during a set-up phase before the tool can be used.
Although spin-pull tools are the better choice for thick wall parts, problems persist with this type of tool. Pull-to-distance tools must have their stroke set properly in order to install an insert, and a certain level of skill and understanding is required to set the stroke. Also, once set-up, pull-to-distance tools can only install inserts into one grip thickness. Another problem is that pull-to-force tools require setting the force so that it is high enough to ensure that all inserts will be installed, but not so high as to damage any inserts with the excessive force. A certain level of skill and understanding is required to properly set the force. Furthermore, tools using a closed hydraulic system will no longer achieve full stroke after a certain amount of hydraulic fluid has leaked out of the system. If not detected immediately, this can lead to under-installed inserts. Even if detected immediately, downtime will occur while hydraulic fluid is added.
There is therefore a need in the art to provide a spin-pull type of tool which is most suitable for thick-walled applications which overcomes the disadvantages of prior art spin-pull type tools for installing blind threaded fasteners.